Astrophysics > Solar and Stellar Astrophysics

Abstract: The CoRoT space telescope observed nearly 160 000 light curves. Among the
most outstanding is that of the young, active planet host star CoRoT-2A. In
addition to deep planetary transits, the light curve of CoRoT-2A shows strong
rotational variability and a superimposed beating pattern. To study the stars
that produce such an intriguing pattern of photometric variability, we
identified a sample of eight stars with rotation periods between 0.8 and 11
days and photometric variability amplitudes of up to 7.5 %, showing a similar
CoRoT light curve. We also obtained high-resolution follow-up spectroscopy with
TNG/SARG and carried out a spectral analysis with SME and MOOG. We find that
the color dependence of the light curves is consistent with rotational
modulation due to starspots and that latitudinal differential rotation provides
a viable explanation for the light curves, although starspot evolution is also
expected to play an important role. Our MOOG and SME spectral analyses provide
consistent results, showing that the targets are dwarf stars with spectral
types between F and mid-K. Detectable Li i absorption in four of the targets
confirms a low age of 100-400 Myr also deduced from gyrochronology. Our study
indicates that the photometric beating phenomenon is likely attributable to
differential rotation in fast-rotating stars with outer convection zones.